Significance of monazite EPMA ages from the Quamby Conglomerate, Queensland
- Evins, P. M., Wilde, A. R., Foster, David, McKnight, Stafford, Blenkinsop, T. G.
- Authors: Evins, P. M. , Wilde, A. R. , Foster, David , McKnight, Stafford , Blenkinsop, T. G.
- Date: 2007
- Type: Text , Journal article
- Relation: Australian Journal of Earth Sciences Vol. 54, no. 1 (2007), p. 19-26
- Full Text:
- Reviewed:
- Description: Th-U-Pb electron microprobe (EPMA) dating of mainly detrital monazite from the Quamby Conglomerate in the Eastern Succession of the Mt Isa inlier reveals three distinct monazite growth/recrystallisation events at around 1640, 1580 and 1490 Ma. These ages are particularly significant with respect to the timing of deposition, iron and gold mineralisation, and deformation in the Mt Isa inlier. The oldest age probably represents provenance from igneous rocks. In the sample, the majority of monazite growth occurred at 1580 Ma, coeval with peak metamorphism in the Eastern Succession. The low metamorphic grade of the conglomerate and wide compositional range of monazite bearing this age indicates that the monazite grew elsewhere and was later deposited in the conglomerate. Purple bands in the rock are composed mainly of coarse specular hematite with recrystallised margins that contribute to high (up to 20%) Fe2O3 contents in the conglomerate. Gold is also present in some of the samples. Some of the monazite grains contain small, younger (ca 1490 Ma) domains that may have grown/ recrystallised in situ during a lower grade syn- or post-diagenetic metamorphic/hydrothermal event that may have been related to hematite (re)crystallisation. Together, these ages bracket deposition of the Quamby Conglomerate to between ca 1580 and 1490 Ma, the latter age most likely representing diagenesis. This depositional age also represents a maximum age for north-south-striking, upright folds of the Quamby Conglomerate and implies that significant ductile deformation has affected parts of the Mt Isa inlier after 1580 Ma and probably after 1490 Ma.
- Description: C1
- Description: Creative work
- Description: 2003004832
- Authors: Evins, P. M. , Wilde, A. R. , Foster, David , McKnight, Stafford , Blenkinsop, T. G.
- Date: 2007
- Type: Text , Journal article
- Relation: Australian Journal of Earth Sciences Vol. 54, no. 1 (2007), p. 19-26
- Full Text:
- Reviewed:
- Description: Th-U-Pb electron microprobe (EPMA) dating of mainly detrital monazite from the Quamby Conglomerate in the Eastern Succession of the Mt Isa inlier reveals three distinct monazite growth/recrystallisation events at around 1640, 1580 and 1490 Ma. These ages are particularly significant with respect to the timing of deposition, iron and gold mineralisation, and deformation in the Mt Isa inlier. The oldest age probably represents provenance from igneous rocks. In the sample, the majority of monazite growth occurred at 1580 Ma, coeval with peak metamorphism in the Eastern Succession. The low metamorphic grade of the conglomerate and wide compositional range of monazite bearing this age indicates that the monazite grew elsewhere and was later deposited in the conglomerate. Purple bands in the rock are composed mainly of coarse specular hematite with recrystallised margins that contribute to high (up to 20%) Fe2O3 contents in the conglomerate. Gold is also present in some of the samples. Some of the monazite grains contain small, younger (ca 1490 Ma) domains that may have grown/ recrystallised in situ during a lower grade syn- or post-diagenetic metamorphic/hydrothermal event that may have been related to hematite (re)crystallisation. Together, these ages bracket deposition of the Quamby Conglomerate to between ca 1580 and 1490 Ma, the latter age most likely representing diagenesis. This depositional age also represents a maximum age for north-south-striking, upright folds of the Quamby Conglomerate and implies that significant ductile deformation has affected parts of the Mt Isa inlier after 1580 Ma and probably after 1490 Ma.
- Description: C1
- Description: Creative work
- Description: 2003004832
Nature of gold mineralisation in the Walhalla Goldfield, southeast Australia
- Hough, M. A., Bierlein, Frank, Ailleres, L., McKnight, Stafford
- Authors: Hough, M. A. , Bierlein, Frank , Ailleres, L. , McKnight, Stafford
- Date: 2010
- Type: Text , Journal article
- Relation: Australian Journal of Earth Sciences Vol. 57, no. 7 (2010), p. 969-992
- Full Text: false
- Reviewed:
- Description: The Walhalla-Woods Point Goldfield in southeast Australia is characterised by large gold deposits associated with a Late Devonian dyke swarm. The setting of this goldfield is unique because unlike the major gold deposits in Victoria, it occurs close to the eastern margin of the Western Lachlan Orogen, and highlights the disparities between the evolving phases of orogenic gold mineralisation in the Western Lachlan Orogen, and the contrasts between sediment hosted, dyke-associated and dyke-hosted gold mineralisation. This study integrates existing and new data from renewed mapping of the geology and geochemistry of three gold deposits near the township of Walhalla, in the historically important yet under-explored and under-researched Walhalla-Woods Point Goldfield. The ten highest yielding deposits within the goldfield are either hosted within, or adjacent to, intrusions of the Woods Point Dyke Swarm. This is due to the greater chemical reactivity of the calc-alkaline dykes, and the greater rheological contrast between the dykes and surrounding low-grade metasedimentary units, which allowed for the formation of dyke-hosted quartz breccia veins that are consistently favourable sites for gold mineralisation in the Walhalla Goldfield. This is in contrast to historical production, which concentrated on visible gold within the shear zone-hosted laminated quartz veins. Gold and As assay results have highlighted the increased levels of invisible gold disseminated along dyke margins in proximity to shear zones and quartz reefs. The high-yielding gold deposits hosted wholly by the dyke intrusions of the Woods Point Dyke Swarm are orogenic gold deposits, as they are not associated with elevated levels of Bi, W, As, Mb, Te and Sb, typical of intrusion-related gold deposits.
- Description: 2003008285
- Mills, Keely, Gell, Peter, Gergis, Joelle, Baker, Patrick J., Finlayson, C. Max, Hesse, Paul, Jones, R., Kershaw, Peter, Pearson, Stuart, Treble, Pauline, Barr, Cameron, Brookhouse, Matthew, Drysdale, Russell, McDonald, Janece, Haberle, Simon, Reid, Michael, Thoms, M., Tibby, John
- Authors: Mills, Keely , Gell, Peter , Gergis, Joelle , Baker, Patrick J. , Finlayson, C. Max , Hesse, Paul , Jones, R. , Kershaw, Peter , Pearson, Stuart , Treble, Pauline , Barr, Cameron , Brookhouse, Matthew , Drysdale, Russell , McDonald, Janece , Haberle, Simon , Reid, Michael , Thoms, M. , Tibby, John
- Date: 2013
- Type: Text , Journal article
- Relation: Australian Journal of Earth Sciences Vol. 60, no. 5 (2013), p. 561-571
- Full Text: false
- Reviewed:
- Description: The management of the water resources of the Murray-Darling Basin (MDB) has long been contested, and the effects of the recent Millennium drought and subsequent flooding events have generated acute contests over the appropriate allocation of water supplies to agricultural, domestic and environmental uses. This water-availability crisis has driven demand for improved knowledge of climate change trends, cycles of variability, the range of historical climates experienced by natural systems and the ecological health of the system relative to a past benchmark. A considerable volume of research on the past climates of southeastern Australia has been produced over recent decades, but much of this work has focused on longer geological time-scales, and is of low temporal resolution. Less evidence has been generated of recent climate change at the level of resolution that accesses the cycles of change relevant to management. Intra-decadal and near-annual resolution (high-resolution) records do exist and provide evidence of climate change and variability, and of human impact on systems, relevant to natural-resource management. There exist now many research groups using a range of proxy indicators of climate that will rapidly escalate our knowledge of management-relevant, climate change and variability. This review assembles available climate and catchment change research within, and in the vicinity of, the MDB and portrays the research activities that are responding to the knowledge need. It also discusses how paleoclimate scientists may better integrate their pursuits into the resource-management realm to enhance the utility of the science, the effectiveness of the management measures and the outcomes for the end users.
- Description: C1
- Mills, Keely, Gell, Peter, Hesse, Paul, Jones, R., Kershaw, Peter, Drysdale, Russell, McDonald, Janece
- Authors: Mills, Keely , Gell, Peter , Hesse, Paul , Jones, R. , Kershaw, Peter , Drysdale, Russell , McDonald, Janece
- Date: 2013
- Type: Text , Journal article
- Relation: Australian Journal of Earth Sciences Vol. 60, no. 5 (2013), p. 547-560
- Full Text: false
- Reviewed:
- Description: This paper provides an incisive review of paleoclimate science and its relevance to natural-resource management within the Murray-Darling Basin (MDB). The drought of 1997-2010 focussed scientific, public and media attention on intrinsic climate variability and the confounding effect of human activity, especially in terms of water-resource management. Many policy and research reviews make statements about future planning with little consideration of climate change and without useful actionable knowledge. In order to understand future climate changes, modellers need, and demand, better paleoclimate data to constrain their model projections. Here, we present an insight into a number of existing long-term paleoclimate studies relevant to the MDB. Past records of climate, in response to orbital forcing (glacial-interglacial cycles) are found within, and immediately outside, the MDB. High-resolution temperature records, spanning the last 105 years, exist from floodplains and cave speleothems, as well as evidence from lakes and their associated lunettes. More recently, historical climate records show major changes in relation to El Niño-Southern Oscillation cycles and decadal shifts in rainfall regimes. A considerable body of research currently exists on the past climates of southeastern Australia but, this has not been collated and validated over large spatial scales. It is clear that a number of knowledge gaps still exist, and there is a pressing need for the establishment of new paleoclimatic research within the MDB catchment and within adjacent, sensitive catchments if past climate science is to fulfil its potential to provide policy-relevant information to natural-resource management into the future. © 2013 Copyright Taylor and Francis Group, LLC.
- Description: C1
Evolution of the boundary between the western and central Lachlan Orogen : Implications for tasmanide tectonics
- Spaggiari, Catherine, Gray, David, Foster, David, McKnight, Stafford
- Authors: Spaggiari, Catherine , Gray, David , Foster, David , McKnight, Stafford
- Date: 2003
- Type: Text , Journal article
- Relation: Australian Journal of Earth Sciences Vol. 50, no. 5 (2003), p. 725-749
- Full Text:
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- Description: Differences in oblique overprinting, along-strike complexity as well as structural, metamorphic and timing constraints suggest that the boundary between the western and central subprovinces of the Lachlan Orogen, currently designated by the Governor Fault, cannot be a single structure. Previously limited data on the nature and kinematics of the fault/shear systems defining the boundary have led to varying scenarios for the tectonic evolution of the Lachlan Orogen. These scenarios either involve large-scale strike-slip displacement along the boundary with subsequent overthrusting or convergence of oppositely vergent thrust-systems with limited strike-slip translation. Geometrical constraints, fabric chronology and kinematic indicators in both the Mt Wellington (Melbourne Zone) and Governor (Tabberabbera Zone) Fault Zones indicate that maximum displacements relate to thrusting and duplex formation, followed by minor strike-slip faulting perhaps in response to slightly oblique collision of the Melbourne and Tabberabbera structural zones. Collision of these zones took place between ca 400 and 390 Ma. At Howqua, structural relationships indicate that collision involved northeast-directed thrusting of the Melbourne Zone (Mt Wellington Fault Zone) over the Tabberabbera Zone (Governor Fault Zone), and was followed by regional, northwest-trending, open folding. These structures overprint the dominant fabrics and metamorphic assemblages that are interpreted to relate to disruption and underthrusting of Cambrian oceanic/arc crust during closure of a marginal basin. Major deformation in the Tabberabbera Zone took place from ca 445 Ma and was associated with mélange formation, underplating and imbrication or duplexing (Governor Fault Zone, East Howqua segmennt). At slightly higher crustal levels, and following deposition of Upper Ordovician black shale and chert sequences (ca 440 Ma), Tabberabbera Zone evolution included offscraping of a serpentinite body (Dolodrook segment) that may have been either a Marianas-style seamount or transform fault zone within the Cambrian oceanic/arc crust. Major thrusting in the Mt Wellington Fault Zone was underway sometime after ca 420 Ma, and in contrast to the Governor Fault Zone, no mélange or broken formation was produced, metamorphism was at slightly higher temperatures and deformation probably occurred under higher strain states.
- Description: C1
- Description: 2003000547
- Authors: Spaggiari, Catherine , Gray, David , Foster, David , McKnight, Stafford
- Date: 2003
- Type: Text , Journal article
- Relation: Australian Journal of Earth Sciences Vol. 50, no. 5 (2003), p. 725-749
- Full Text:
- Reviewed:
- Description: Differences in oblique overprinting, along-strike complexity as well as structural, metamorphic and timing constraints suggest that the boundary between the western and central subprovinces of the Lachlan Orogen, currently designated by the Governor Fault, cannot be a single structure. Previously limited data on the nature and kinematics of the fault/shear systems defining the boundary have led to varying scenarios for the tectonic evolution of the Lachlan Orogen. These scenarios either involve large-scale strike-slip displacement along the boundary with subsequent overthrusting or convergence of oppositely vergent thrust-systems with limited strike-slip translation. Geometrical constraints, fabric chronology and kinematic indicators in both the Mt Wellington (Melbourne Zone) and Governor (Tabberabbera Zone) Fault Zones indicate that maximum displacements relate to thrusting and duplex formation, followed by minor strike-slip faulting perhaps in response to slightly oblique collision of the Melbourne and Tabberabbera structural zones. Collision of these zones took place between ca 400 and 390 Ma. At Howqua, structural relationships indicate that collision involved northeast-directed thrusting of the Melbourne Zone (Mt Wellington Fault Zone) over the Tabberabbera Zone (Governor Fault Zone), and was followed by regional, northwest-trending, open folding. These structures overprint the dominant fabrics and metamorphic assemblages that are interpreted to relate to disruption and underthrusting of Cambrian oceanic/arc crust during closure of a marginal basin. Major deformation in the Tabberabbera Zone took place from ca 445 Ma and was associated with mélange formation, underplating and imbrication or duplexing (Governor Fault Zone, East Howqua segmennt). At slightly higher crustal levels, and following deposition of Upper Ordovician black shale and chert sequences (ca 440 Ma), Tabberabbera Zone evolution included offscraping of a serpentinite body (Dolodrook segment) that may have been either a Marianas-style seamount or transform fault zone within the Cambrian oceanic/arc crust. Major thrusting in the Mt Wellington Fault Zone was underway sometime after ca 420 Ma, and in contrast to the Governor Fault Zone, no mélange or broken formation was produced, metamorphism was at slightly higher temperatures and deformation probably occurred under higher strain states.
- Description: C1
- Description: 2003000547
Leven Star deposit: An example of Middle to Late Devonian intrusion-related gold systems in the western Lachlan Orogen, Victoria
- Whittam, R. R., Bierlein, Frank, McKnight, Stafford
- Authors: Whittam, R. R. , Bierlein, Frank , McKnight, Stafford
- Date: 2006
- Type: Text , Journal article
- Relation: Australian Journal of Earth Sciences Vol. 53, no. 2 (2006), p. 343-362
- Full Text:
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- Description: This study documents an example of atypical gold mineralisation in the central Victorian gold province of the western Lachlan Orogen, Australia. Unlike the vast majority of orogenic gold deposits in this region, the Leven Star deposit at Malmsbury is characterised by a disseminated-stockwork style of mineralisation, a close spatial and temporal association with post-tectonic felsic intrusions, complex alteration characteristics and a Au-As-Sb (±Bi-Te-Cu-Zn-Pb-Sn-W) ore assemblage. In contrast to orogenic-style, metamorphism-related gold mineralisation (ca 440 Ma), which pre-dated magmatism in the western Lachlan Orogen by tens of millions of years, ore formation in the Leven Star deposit was synchronous with, and is paragenetically younger than, Middle to Late Devonian (ca 370 Ma) magmatism. On the basis of these timing relationships, as well as whole-rock geochemistry, and structural, petrographic and fluid-inclusion data, it is suggested that the Leven Star deposit is not orogenic in character and instead should be classified as intrusion-related. © Geological Society of Australia.
- Description: C1
- Description: 2003001628
- Authors: Whittam, R. R. , Bierlein, Frank , McKnight, Stafford
- Date: 2006
- Type: Text , Journal article
- Relation: Australian Journal of Earth Sciences Vol. 53, no. 2 (2006), p. 343-362
- Full Text:
- Reviewed:
- Description: This study documents an example of atypical gold mineralisation in the central Victorian gold province of the western Lachlan Orogen, Australia. Unlike the vast majority of orogenic gold deposits in this region, the Leven Star deposit at Malmsbury is characterised by a disseminated-stockwork style of mineralisation, a close spatial and temporal association with post-tectonic felsic intrusions, complex alteration characteristics and a Au-As-Sb (±Bi-Te-Cu-Zn-Pb-Sn-W) ore assemblage. In contrast to orogenic-style, metamorphism-related gold mineralisation (ca 440 Ma), which pre-dated magmatism in the western Lachlan Orogen by tens of millions of years, ore formation in the Leven Star deposit was synchronous with, and is paragenetically younger than, Middle to Late Devonian (ca 370 Ma) magmatism. On the basis of these timing relationships, as well as whole-rock geochemistry, and structural, petrographic and fluid-inclusion data, it is suggested that the Leven Star deposit is not orogenic in character and instead should be classified as intrusion-related. © Geological Society of Australia.
- Description: C1
- Description: 2003001628
- Wilson, C., McKnight, Stafford, Dugdale, A., Rawling, T., Farrar, A., McKenzie, M., Melling, W.
- Authors: Wilson, C. , McKnight, Stafford , Dugdale, A. , Rawling, T. , Farrar, A. , McKenzie, M. , Melling, W.
- Date: 2009
- Type: Text , Journal article
- Relation: Australian Journal of Earth Sciences Vol. 56, no. 8 (2009), p. 1143-1164
- Full Text: false
- Reviewed:
- Description: Gold mineralisation in the Lachlan Orogen of western Victoria, is generally hosted in turbidites with very low-grade metamorphic assemblages. Metamorphic data from these turbidites are relatively rare because of the fine-grained nature of the pelitic component and lack of suitable assemblages for thermobarometric estimates. In this study, 'illite crystallinity' (Kubler Index) and b-lattice spacing measurements were carried out on white micas in metapelites, collected from near the inferred western margin of the Selwyn Block, as well as three exploration targets, in an attempt to relate thermal and barometric conditions to mineralisation. Higher-grade (epizone) metamorphic conditions are recorded in sequences west of the Whitelaw Fault and lower-grade (anchizone) metamorphic conditions to the east of the fault. The change from epizonal to anchizonal grade is abrupt, resolved to a distance of a few hundred metres. The b-spacing values change adjacent to the Muckleford Fault. This is due to rocks to the east being exhumed as the edge of the Selwyn Block moved westward during the Middle Devonian Tabberabberan Orogeny at 380Ma. We propose that the juxtaposition of rocks with contrasting thermal and barometric histories represents expression of the upper crustal location of the western margin of the Selwyn Block at the time of peak deformation, at about 440Ma, and this crustal structure controlled the distribution of the major quartz-vein-type gold deposits. The Middle Devonian orogenic activity (380Ma) was accompanied by the formation of disseminated gold deposits such as Fosterville. This represents a mineralising event that overprints the earlier gold deposits in a corridor at least 50km wide and to the west of the Whitelaw Fault, that parallels the margin of the Selwyn Block. The correlation between gold assays and 'illite crystallinity' results, from X-ray diffraction and from short-wave infrared-reflectance field-spectroscopy data, were ambiguous. Kubler Indices are not found to be effective in targeting of mineralisation as the values obtained from the alteration and the host-rock assemblages were similar and reflected the ambient P-T conditions at the time of mineralisation.
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